题目：https://vjudge.net/problem/UVA-11059

set<int,greater<int> > s;

s中元素默认从大到小排列

ac代码：

#include <iostream>
#include <cmath>
#include <cstring>
#include <cctype>
#include <algorithm>
#include <stdlib.h>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <sstream>
using namespace std;
typedef long long ll;
int main()
{
    ll n,s[20],i,j,num=0,mul;
    //freopen("/Users/zhangkanqi/Desktop/11.txt","r",stdin);
    while(scanf("%lld",&n)==1)
    {
        num++;
        set<ll,greater<ll> > ans;
        for(i=0;i<n;i++)
        {
            scanf("%lld", &s[i]);
            ans.insert(s[i]);
        }
        for(i=0;i<n;i++)
        {
            mul=s[i];
            for(j=i+1;j<n;j++)
            {
                mul*=s[j];
                ans.insert(mul);
            }
        }
        set<ll,greater<ll>>::iterator it=ans.begin();
        printf("Case #%d: The maximum product is %lld.\n\n",num,*it<0?0:*it);
    }
    return 0;
}

网上的代码，思路不同：

#include<iostream>
#include<cstdio>
using namespace std;
long long num[100];
 
int main()
{
	int n;
	int cnt = 0;
	while (cin >> n)
	{
		long long ans = 0;
		for (int i = 0; i < n; ++i)
			cin >> num[i];
		for (int i = 1; i <= n; ++i) //i:子序列长度 
		{
			for (int j = 0; j + i <= n; ++j) //j:子序列起点 （这里之前写j + i < n，怒跪） 
			{
				long long tt = 1;
				for (int k = j; k < j + i; ++k) //累乘 
				{
					tt *= num[k];
				}
				//cout << tt << endl;
				ans = max(ans, tt);
			}
		}
		printf("Case #%d: The maximum product is %lld.\n\n", ++cnt, ans);
	}
	return 0;
}